Primary pressure-balanced proportioning valve

ABSTRACT

The proportioning valve assembly (40, 140) may be screwed into a complementary-shaped opening in a master cylinder (10). The valve assembly (40, 140) includes a differential area piston (50, 150) biased by a spring (70, 170) toward the outlet (21, 121) which communicates with the rear brakes. The master cylinder (10) includes a pair of passageways (16, 18) which communicate primary fluid pressure and secondary fluid pressure directly to the differential area piston (50, 150) of the proportioning valve assembly (40, 140) to displace the piston (50, 150) to a balanced position. If there is a failure of pressure in the primary brake circuit, the proportioning valve assembly (40, 140) actuates the differential area piston (50, 150) to permit fluid flow to bypass the piston (50, 150) and be communicated directly to the rear brakes of the vehicle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a proportioning valve utilized incombination with a master cylinder, in particular a proportioning valvewhose piston is actuated by fluid pressure received directly from theprimary and secondary pressure chambers of the master cylinder.

2. Description of the Prior Art

In general, proportioning valves utilize a differential area piston inthe secondary chamber brake system so that when a predetermined pressurelevel is reached, the piston shifts in the direction of the smaller areaproportioning valve piston end. As the piston shifts, the pistoncontacts a poppet or seal and thus establishes a pressure restriction.Upon a further increase in secondary pressure communicated to theproportioning valve piston, the outlet pressure will rise at a ratedetermined by the differential areas at each end of the piston.

A proportioning valve may be coupled with the master cylinder by meansof a threaded connection. The proportioning valve includes a bypassfunction so that upon failure of pressure in a chamber of the mastercylinder, the proportioning valve responds appropriately and permitsfluid pressure to be communicated freely to the rear brakes of thevehicle. Such existing designs contain numerous disadvantages such as:the primary and secondary pressure chambers of the master cylinder mustbe reversed which lengthens the master cylinder body; the mastercylinder being stroke sensitive rather than pressure sensitive; theutilization of mechanical actuation instead of hydraulic actuation;numerous parts required for the assembly which results in high cost; anda bypass mechanism that is subject to many manufacturing tolerances andpossibly subject to damage. It is highly desirable to provide aproportioning valve assembly with a bypass feature wherein it is notnecessary to switch the position of the primary and secondary chambersin the master cylinder. It is also desirable to actuate theproportioning valve assembly by communicating directly pressure from theprimary pressure chamber of the master cylinder to the proportioningvalve assembly.

SUMMARY OF THE INVENTION

The present invention utilizes a differential area piston with one endof the piston acted upon directly by primary pressure received from themaster cylinder. The other, larger diameter, end of the piston is actedupon directly by pressure received from the secondary chamber of themaster cylinder. The secondary chamber fluid pressure is proportionedduring actuation of the proportioning valve. The large diameter end ofthe piston is essentially pressure balanced after reaching the breakpoint due to secondary outlet pressure acting on the larger diameter endand the primary pressure acting on the piston's small diameter end.Because the master cylinder primary and secondary pressures on thepiston are essentially equal by utilizing the primary pressure tobalance the proportioning valve piston, when the primary pressure failsthe piston forces become unbalanced and thus shift the piston to aposition wherein a bypass circuit is effected so that secondary pressureis communicated freely through the secondary outlet.

The present invention comprises a proportioning valve in combinationwith a master cylinder the master cylinder comprising a primary pressurechamber and a secondary pressure chamber, communication means forcommunicating fluid pressure from the respective pressure chambers to atransverse bore having said proportioning valve disposed therein, thebore having at one end a primary pressure receiving chamber locatedradially inwardly relative to the master cylinder and at the other end asecondary pressure receiving chamber located radially outwardly, thesecondary pressure receiving chamber having an outlet opening, adifferential area piston disposed within said bore and having a primaryend received in the primary pressure receiving chamber and a secondaryend received in the secondary pressure receiving chamber, the primaryend having at least one seal thereabout in order to define a part of theprimary pressure receiving chamber, the secondary end having sealingmeans disposed thereabout, resilient means disposed between said pistonand a shoulder of said bore, the differential area piston comprising afirst piston part and a second piston part, the first piston part havingan extension extending into a through opening of the second piston, theextension having a seal member thereabout and the seal member alignedwith a radial opening in the second piston part and engaging sealingly ashoulder of the second piston part, so that failure of pressure in theprimary chamber causes the first piston part to be displaced and movethe seal member from sealing engagement with the shoulder to permitfluid pressure in the second pressure receiving chamber to becommunicated through the radial opening and through opening in thesecond part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to thedrawings which illustrate embodiments in which:

FIG. 1 is a section view of the proportioning valve and master cylinderof the present invention;

FIG. 2 is a section view of the preferred embodiment;

FIG. 3 is an enlarged section view of a portion of FIG. 2; and

FIG. 4 is a section view of an alternative embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The master cylinder is designated generally by reference numeral 10 inFIG. 1. The master cylinder is of the type designated "RecessedCartridge Master Cylinder" and disclosed in U.S. Pat. No. 4,474,005. Itshould be clearLy understood that the present invention may be utilizedwith many other types of master cylinders, and is not restricted to usewith just a Recessed Cartridge Master Cylinder. The master cylinder 10includes a primary chamber (not shown) located interiorily of an end 12and a secondary chamber (not shown) located interiorily of end 14. Apassageway or communication means 16 extends from the primary chamber toa primary pressure receiving chamber 26 located within master cylinderhousing 11. A passageway or communication means 18 extends between thesecondary pressure chamber and a secondary pressure receiving chamber 28located within housing 11. A vent 19 may extend to either atmosphere orto a reservoir (not shown) of the master cylinder. The proportioningvalve assembly is designated generally by reference numeral 40 andcomprises a valve housing part 42 received threadably in transverse bore13 of housing 11. Bore 13 comprises a stepped bore which extends fromthe primary pressure receiving chamber 26 to the secondary pressurereceiving chamber 28. Proportioning valve assembly 40 includes a valvehousing part 43 clasped to first housing part 42 by means of a flange44. Stepped bore 13 provides a shoulder 15 for engagement by a seal 46disposed about differential area piston 50. Differential area piston 50includes a first piston part 52 and second piston part 54. First pistonpart 52 includes an extension 53 received within a through opening 56 ofsecond piston part 54. Extension 53 includes a seal 55 disposedthereabout, the seal blocking fluid flow between a radial opening 57 andthrough opening 56 in second piston part 54. The second piston part 54has a seal 45 disposed thereabout and engaging the interior of secondhousing part 43. Resilient means 70 extends between a second housingshoulder 48 and a flange 61 of second piston part 54. A seal 47 isdisposed about the exterior of second housing part 43 and engages ashoulder 17 of housing 11. The second piston part 54 has an end 58 whichabuts shoulder 49 of housing part 42. Piston end 58 includes sealingmeans 72 disposed thereabout. Sealing means 72 has a flexible pumpingarm 73, radial passageways 74, and spaced apart circumferentialabutments 75. The interior diameter of resilient sealing means 72 isspaced radially apart from the exterior surface of circumferentialgroove 59 of piston second part 54. Each of the seals disposed about theexterior of assembly 40 is a static seal which engages a portion ofstepped bore 13 when valve assembly 40 is threadably received withinhousing 11.

Proportioning valve assembly 40 is shown in an at-rest position. Whenmaster cylinder 10 is actuated by the vehicle operator depressing thebrake pedal of the vehicle, primary and secondary chamber fluid pressureis communicated by means of passageways 16 and 18 to the respectivepressure receiving chambers 26 and 28. Because of the diameters ofdifferential area piston 50, the secondary pressure displaces piston 50slightly toward the left in FIG. 1, against the force of resilient means70 and the primary fluid pressure in chamber 26 acting upon first pistonpart 52. Upon an increase of fluid pressures received in chambers 26 and28, piston 50 is displaced to the left until the outer diameter ofpiston end 58 engages sealing means 72. This causes a restriction ormetering of fluid pressure communicated between passageway 18,pressure-receiving chamber 28, and secondary outlet 21. It should benoted that prior to the leftward movement of the piston 50, theabutments 75 on sealing means 72 ensures that fluid pressure is free topass between the interior diameter of sealing means 72 andcircumferential groove 59 to the secondary outlet 21. As shown ingreater detail in FIG. 3, seal 55 has a generally L-shaped section andengages shoulder 51 of second piston part 54. Seal 55 avoids contactwith radial opening 57 so that opening 57 cannot cut or gouge out partsof seal 55. Thus, sealing is accomplished at shoulder 51 so that fluiddoes not flow through opening 56. Should there be a failure of pressurein the primary chamber of master cylinder 10, an unbalancing of forcesis created and first piston part 52 moves immediately leftward inchamber 26 which causes extension 53 to move seal 55 out of sealingengagement with shoulder 51. This permits fluid pressure withinsecondary pressure receiving chamber 28 to be communicated throughradial opening 57 and through opening 56 to outlet 21 so that a bypassfunction is accomplished and full braking pressure may be communicatedto the rear brakes of the vehicle. As a result of communicating themaster cylinder primary chamber pressure directly to the differentialarea piston of the proportioning valve assembly, there is no longerrequired the utilization of primary pressure to indirectly effect abypass by means of other intermediate mechanisms. The fluid pressurefrom the primary chamber of the master cylinder acts directly upon theproportioning valve piston to eliminate any need for reversing theprimary and secondary chambers of the master cylinder. No externalmechanical mechanisms are required in order to actuate the proportioningvalve assembly and effect the bypass function. The primary pressure isrequired for operation of the proportioning valve assembly. However,should there be a failure of fluid pressure in the primary brakingcircuit, the proportioning valve assembly actuates immediately to effectthe bypass feature and permit the direct communication of full fluidpressure to secondary outlet 21 and the rear brakes of the vehicle.

FIG. 4 illustrates an alternative embodiment, and similar structure isindicated by the same reference numeral increased by 100. The piston 150comprises a single part, integral piston having disposed thereabout asleeve or second housing part 143 which includes a flange 180 whichsnaps together with flange 182 of first housing part 142. The vent 119communicates with either the reservoir 190 or with atmosphere.Proportioning valve assembly 140 operates as described above except thatupon failure of fluid pressure in the primary chamber of the mastercylinder and primary pressure receiving chamber 126, the entire piston150 moves to the left in FIG. 4 and displaces end 158 through theinterior diameter of sealing means 172. Fluid pressure in secondarypressure receiving chamber 128 may then communicate past the insidediameter of sealing means 172 and through slots 159 of piston 150 tosecondary outlet 121.

The proportioning valve assembly and master cylinder of the presentinvention comprises a substantial improvement over prior constructions.Because the primary chamber fluid pressure is utilized to actuate andoperate directly the proportioning valve assembly, intermediatemechanisms and devices and reversal of the pressure chambers of themaster cylinder are obviated. An additional advantage is that theproportioning valve assembly and master cylinder permit thecommunication of greater fluid pressure to the rear brakes of thevehicle when such can be tolerated. In other words, the break point onthe pressure curve may be led or lagged according to designmodification. In actual operation, the fluid pressures communicated fromthe primary and secondary chambers of the master cylinder are slightlydifferent, in the magnitude of approximately 20 to 30 psi. The fluidpressure variance communicated from the primary pressure chamber of themaster cylinder is approximately 20 to 30 psi. lower than the fluidpressure communicated from the secondary pressure chamber. This is aresult of difference in spring loads and seal friction. Thus, duringactual braking, the front brakes of the vehicle receive slightly lesspressure than the rear brakes of the vehicle receive initially.Therefore, the front brakes are slightly less effective and there is nota shifting of the load off the rear wheels, i.e., the rear portion ofthe vehicle does not tilt to the extent that it might if the pressurestransmitted from the primary and secondary pressure chambers wereactually equal. Because of reduced tilting of the vehicle, the rearwheels of the vehicle can tolerate more fluid pressure. In the presentinvention, the initial slight leftward movement of the differential areapiston allows a greater amount of pressure to the rear brakes. Thiseffects a raising of the break-point of the characteristic outputpressure curve.

While the invention has been described with respect to the detailedembodiments, it will be understood that the invention is capable ofnumerous rearrangements, modifications, and alterations, and such areintended to be within the scope of the appended claims. It is reasonablyto be expected that those skilled in the art can make numerous revisionsand additions to the invention and it is intended that such revisionsand additions will be included in the scope of the following claims asequivalents of the invention.

We claim:
 1. A proportioning valve in combination with a mastercylinder, the master cylinder comprising a primary pressure chamber anda secondary pressure chamber, communication means for communicatingfluid pressure from the respective pressure chambers to a transversebore having said proportioning valve disposed therein, the bore havingat one end a primary pressure receiving chamber located radiallyinwardly relative to the master cylinder and at the other end asecondary pressure receiving chamber located radially outwardly, thesecondary pressure receiving chamber having an outlet opening, adifferential area piston disposed within said bore and having a primaryend received in the primary pressure receiving chamber and a secondaryend received in the secondary pressure receiving chamber, the primaryend having at least one seal thereat in order to define a part of theprimary pressure receiving chamber, the secondary end having sealingmeans disposed thereat, resilient means disposed between said piston anda shoulder in said bore, the differential area piston comprising a firstpiston part and a second piston part, the first piston part having anextension received at a through opening of the second piston part, theextension having a seal member thereabout, and the seal member adjacenta radial opening in the second piston part and engaging sealingly a partof the second piston part, and a stepped, stationary sleeve located insaid bore and disposed about said first and second piston parts in orderto define a portion of a vented intermediate chamber, so that failure ofpressure in the primary chamber causes the first piston part to bedisplaced and the seal member to move from sealing engagement to permitfluid pressure in the second pressure receiving chamber to becommunicated through the radial opening and the through opening in thesecond part.
 2. The proportioning valve and master cylinder inaccordance with claim 1, wherein the through opening in the secondpiston part communicates with the outlet opening.
 3. The proportioningvalve and master cylinder in accordance with claim 2, wherein the boreincludes a second seal spaced apart from the one seal to define a partof the intermediate chamber which communicates with a vent.
 4. Theproportioning valve and master cylinder in accordance with claim 3,wherein the vent communicates with the reservoir.
 5. The proportioningvalve and master cylinder in accordance with claim 3, wherein theintermediate chamber and vent communicate with atmosphere.
 6. Theproportioning valve and master cylinder in accordance with claim 3,wherein the sealing means at the secondary end comprises a flexible armon one side and a plurality of radial slot openings on the other side,the radial slot openings permitting fluid flow therethrough and past theflexible arm during a release of braking pressure.
 7. The proportioningvalve and master cylinder in accordance with claim 6, wherein theresilient means extends between a flange at the secondary end of thepiston and the shoulder in the bore.
 8. The proportioning valve andmaser cylinder in accordance with claim 7, wherein the intermediatechamber extends interiorly of the sleeve.
 9. The proportioning valve andmaster cylinder in accordance with claim 8, wherein a seal mechanism isdisposed between the second piston part and sleeve in order to define apart of the intermediate chamber.
 10. A proportioning valve incombination with a master cylinder, the master cylinder comprising aprimary pressure chamber and a secondary pressure chamber, communicationmeans for communicating fluid pressure from the respective pressurechambers to a bore having said proportioning valve disposed therein, thebore having at one end a primary pressure receiving chamber and at theother end a secondary pressure receiving chamber, the secondary pressurereceiving chamber having an outlet opening, a differential area pistondisposed within said bore and having a primary end received in theprimary pressure receiving chamber and a secondary end received in thesecondary pressure receiving chamber, the primary end having at leastone seal thereat in order to define a part of the primary pressurereceiving chamber, the secondary end having sealing means disposedthereat which controls fluid flow past the secondary end to the outlet,resilient means disposed between said piston and a shoulder in saidbore, the differential area piston comprising a first piston part and asecond piston part, the first piston part having an extension extendinginto a through opening of the second piston part, and the extensionhaving a seal member thereat and the seal member aligned with an openingin the second piston part and engaging sealingly a shoulder of thesecond piston part, and a stepped, stationary sleeve located in the boreand disposed about the first and second piston parts in order to definea portion of a vented intermediate chamber, the communication of fluidpressure from the primary and secondary chambers to the respectivepressure receiving chambers causing said differential area piston to bedisplaced to a substantially balanced position during actuation of saidproportioning valve and failure of pressure in the primary chamberdisplacing the first piston part and seal member to permit fluid to flowthrough the through opening and effectively bypass the sealing means.11. A proportioning valve, the proportioning valve received in a borehaving communication means for receiving fluid pressure communicated tothe bore, the boree having at one end a first pressure receiving chamberand at the other end a second pressure receiving chamber, the secondpressure receiving chamber having an outlet opening, a differential areapiston disposed within said bore and having a first end received in thefirst pressure receiving chamber and a second end received in the secondpressure receiving chamber, the first end having a seal thereat todefine a part of the first pressure receiving chamber, the second endhaving sealing means disposed thereat, the differential area pistoncomprising a first piston part and a second piston part, the firstpiston part having an extension received at a through opening of thesecond piston part, the extension having a seal member and the sealmember controlling fluid flow through a second opening in the secondpiston part, and the second opening communicating with the throughopening, a stepped, stationary sleeve located in said bore and disposedabout said first and second piston parts in order to define a portion ofa vented intermediate chamber, and resilient means biasing said secondpiston part, communication of fluid pressure to the respective pressurereceiving chambers causing said differential area piston to be displacedto a substantially balanced position during actuation of saidproportioning valve and failure of pressure in the first pressurereceiving chamber displacing the first piston part and seal member topermit fluid to flow through the through opening and effectively bypassthe sealing means.
 12. The proportioning valve in accordance with claim11, wherein the bore includes a second seal spaced apart from the sealat the first end to define a portion of the intermediate chamber whichcommunicates with a vent.
 13. The proportioning valve in accordance withclaim 13, wherein the vent communicates with a reservoir.
 14. Theproportioning valve in accordance with claim 1, wherein the intermediatechamber and vent communicate with atmosphere.
 15. The proportioningvalve in accordance with claim 11, wherein the intermediate chamberextends interiorly of the sleeve.
 16. The proportioning valve inaccordance with claim 15, wherein a seal mechanism is disposed betweenthe second piston part and sleeve in order to define a part of theintermediate chamber.
 17. The proportioning valve in accordance withclaim 11, wherein the sealing means about the second end comprises aflexible arm on one side and a plurality of radial slot openings on theother side, the radial slot openings permitting fluid flow therethroughand past the flexible arm during a release of braking pressure.
 18. Theproportioning valve in accordance with claim 17, wherein the resilientmeans extends between a flange at the second piston part and shouldermeans in the bore.
 19. The proportioning valve in accordance with claim18, wherein the proportioning valve includes a housing, the housingscrewed into the bore which is disposed within a master cylinder. 20.The proportioning valve in accordance with claim 19, wherein the housingcomprises two members held together by a flange.